1. Field of the Invention
The present invention relates generally to a mobile communication system, and in particular, to an apparatus and method for transmitting/receiving time information in an idle state in a GSM (Global System for Mobile Communications) communication system by using an idle frame or a stealing flag of a normal burst contained in a Broadcast Control CHannel (BCCH).
2. Description of the Related Art
In general, transmission/reception of time information in mobile communication systems is performed differently depending on the types of access schemes used, such as CDMA (Code Division Multiple Access) and GSM.
In a CDMA communication system, base stations acquire synchronization using a Global Positioning System (GPS) and transmit time information received from the GPS to portable terminals, thereby completing time setting without users' intervention. That is, the CDMA portable terminals can keep accurate time even without users' intervention for time setting.
However, a GSM communication system does not use the GPS. Therefore, in the GSM communication system, time setting in a GSM portable terminal is performed by a user's intervention or by using time information received from a network, and a built-in Real-Time Clock (RTC) is used to maintain the time setting when the GSM portable terminal is turned off. However, the time setting using the built-in RTC is low in reliability. Thus, unlike the CDMA communication system, the GSM communication system requires time correction.
In an optional method, a dedicated channel is used to transmit time information from the GSM network to the GSM portable terminal. The optional method uses an optional message, such as mobility management information message, for transmission of the time information. The optional message is not necessarily to be transmitted from the network, and the dedicated channel causes overhead to the network.
What is therefore required is an apparatus and method that can keep accurate time without causing overhead to the network.